Induction furnaces

ABSTRACT

There is disclosed herein an induction furnace of the submerged resistor type for melting metals wherein a throat is interposed between the hearth and the secondary loop and that portion of the throat at its intersection with a central channel of the secondary loop has a portion of an axial dimension substantially greater than the axial dimension of said center channel and substantially greater than the actual dimension of a bottom channel, said axial dimensions being those parallel to the axis of primary coils threading the secondary loop and each of the channels has a major portion of its length of substantially uniform cross section.

United States Patent Wilbur E. Shearman Cortland. Ohio Jan. 28, 1970 July 27, 197 1 Ajax Magnethermic Corporation Warren, Ohio [72] Inventor [2i Appll No. [22] Filed [45] Patented [73] Assignee [54] INDUCTION FURNACES 2,541,84l 2/l95l Tama 3,092,682 6/l963 Tamaetalm.

Primary Examiner-J. V. Truhe Assistant Examiner-L. H. Bender Attorney-J. H. Slough ABSTRACT: There is disclosed herein an induction furnace of the submergedresistor type for melting metals wherein a throat is interposed between the hearth and the secondary loop and that portion of the throat at its intersection with a PATENTEU m2? I97! SHEET 1 OF 4 //VVNTOR l/l/f/buk E hear nan SLOUGH A TTORNEY INDUCTION-FURNACES My invention relates to the melting of metals in induction furnaces and relates more particularly to an improved method and/or apparatus for melting metals in single ore, twin coil induction furnaces of the submerged resistor type.

My invention relates further to improvements in induction furnaces of the type set forth, described and claimed in US. Pat. No. 3,092,682 granted June 4, I963 to Manuel Tama and the present inventor.

In said prior invention unidirectional flow was achieved in a twin coil induction furnace-and the metal moved from the hearth first at a relatively low temperature through a central channel and then back into the hearth through a bottom or connecting channel into substantially vertical lateral channels at gradually increased melt temperatures and increased velocity.

The furnace of my present design provides substantially increased velocity, increased hearth circulation and a further reduction in the temperature differential between the melt channels and the hearth, as contrasted with the previous construction recited above, and is adapted to utilize by reason of its more rapid flow and lower temperature differentials higher power inputs than possible with prior furnaces of this type. It has particular application in the melting of ferrous and nonferrous metals and their alloys where higher power inputs are used.

In recent years the wide use of detachable inductors has lead to constructions which embody a connecting passage or throat" for the molten metal between the channels where the power is induced and the hearth where the bulk of the metal to be melted is contained therein. For example, see US. Pat. No. 2,520,349 granted Aug. 29, 1950 to M. Tama.

Certain larger furnaces of this type have employed a number of channel induction means and have a plurality of throats communicating with the substantially larger hearth.

I have discovered that when the current carrying portion of the throat connecting the hearth to the central channel is axially widened at its intersection with the central channel having the major portion ofits length of uniform cross section as in an induction furnace of the type shown in US. Pat. No. 3,092,682, referred to above, and the said intersecting portion of the throat held to an axial dimension substantially greater than the'axial dimension of said bottom channel, which axial dimensions are those parallel to the axis of the primary coils, that the velocity of the unidirectional flow is greatly increased and temperatures of metal within the channels considerably lowered.

Conventionally the connecting passages or throats of the prior art have been generally rectangular in form and exceeded the axial width and radial spread of the inductor channels only sufficiently to allow for minor alignment variations in the separately assembled hearth and inductor sections. It has often been found, within the limits of the inductor section that a sub or lower throat is necessary for structural purposes. Its enlargement beyond that of the channels was only sufficient to permit removal of the molds that formed the channels in the ceramic lining. Deviations from this have been employed when lateral support for surrounding walls was provided by a supporting arch at one or both sides of the throat or when a turbulence-dampening element required slidable support at a specific distance from the upper end ofa central channel. An

7 v axial enlargement the full length of the throat at this specific distance was usually employed for this purpose. Such specific distance normally was greater than the radial depth wherein the greatest portion of the secondary currents flowed, i.e. usually in excess of one reference depth for the metal contained therein.

The invention has been found particularly advantageous in higher power channels which are substantially longer than those heretofore used.

It has also been found particularly advantageous in the melting of metals and their alloys such as brass, where there is but slight temperature differential between melting and vaporization.

It is therefore an object of this invention to provide improved means to reduce temperature differentials between the hearth and the secondary loop and to increase the velocity of the flow of metal permitting an increase in the power inputs and operative capacity of the furnace.

Another object of my invention is to increase the rapid exchange of the relatively small amount of molten metal contained within the power generating secondary loop with the bulk ofthe metal contained in the hearth.

It is a further object of my invention to achieve a substantial improvement in the circulatory means, utilizing inherent electromagnetic forces for the motivation.

A still further object of my invention is to achieve the improved temperature differentials and flow in a unidirectional flow furnace with minimum eddies and turbulence in the loop.

Another object of the invention is to achieve improvements in the lining life of the furnace by the higher velocities and lower temperatures of said furnace.

Other objects of this invention and the invention itself will become more readily apparent by reference to the appended description in which description reference will be made to the accompanying drawings,-in which drawings:

FIG. 1 is a vertical section of a first embodiment of the improved induction melting furnace of this invention;

FIG. 2 is a section taken along the line 2-2 of FIG. l;

FIG. 3 is a top plan view of the channel form in the furnace ofFIGS. land 2',

FIG. 4 is a section similar to the lower portion of FIG. 1 showing a second embodiment of the furnace of this invention;

FIG. 5 is a section taken along the line 5-5 of FIG. 4;

FIG. 6 is a top plan view of the channel form in the furnace ofFIGS. 4 and 5;

FIG. 7 is an enlarged perspective of the channel form of FIGS. 13 as viewed from the bottom, side and one end thereof, the modification of FIGS. 4-6 being shown in broken lines;

FIG. 8 is a top plan view similar to FIGS. 3 and 6 showing a further modified channel form;

FIG. 9 is an enlarged perspective sectional view of the furnace of FIG. 4 with a diagram superimposed thereabove showing the temperature pattern when said furnace is operated at the 0-kw. power level;

FIG. 10 is an isometric view showing the outline of a prior art channel form with the corresponding temperature pattern superimposed thereon, the same being a copy of FIG. 5 of U.S. Pat. No. 3,092,682;

FIG. 11 is a perspective sectional view of a furnace constructed generally according to the above prior art patent with a diagram superimposed thereabove showing the temperature pattern when the same is operated at the power level of FIG.

FIG. 12 is an enlarged fragmentary view of portions of FIG. 2 showing the induced current pattern ofthe invention; and

FIG. 13 is an enlarged fragmentary view of portions of FIG. 1 further illustrating the induced current pattern of the inven tion.

Referring now to the drawings, in all of which like parts are designated by like reference characters, it will be noted that the general construction of the furnace of the present invention is similar to the submerged resistor twin coil furnaces illustrated in US Pat. No. 3,092,682. A lengthy description of the principle of operation is, therefore, believed to be unnecessary. The principal parts in FIGS. 1 and 2 are a housing 1, comprising a hearth 2 and a submerged resistor twin coil unit attached thereto. The hearth is adapted to hold the bulk ofa charge of metal to be melted up to the level 2 and is lined with refractory material 3. In the particular designs chosen to illustrate this invention a submerged resistor unit is provided with two loops (twin coil furnace); therefore, three substantially parallel channels 4, 5 and 6 are provided connected at the bottom by a channel portion 7 and connected at the upper ends thereof through a throat l1 and each of the channels, as shown in the prior art patent referred to above, has a major portion ofits length of substantially uniform cross section.

The transformer assembly comprises, in the embodiments illustrated, two coils of insulated copper wire which in operation are connected to a current supply source, such as a singlephase supply source of standard frequency alternating current, not shown. In the drawings, these coils are denominated by the numeral 8. An iron core 10 threads the primary winding and is closed in itself from both sides of the furnace. The transformer assembly is contained in a housing 12 to which a current of air may be passed by a blower 13 for cooling purposes.

The submerged resistor unit is fastened to the hearth unit attached to the flange 14 by bolts or the like.

The furnace has a removable cover I5.

It will be noted that the portion of the throat llimmediately adjacent the upper end of the center channel 5 which channel is of substantially uniform cross section is of substantially greater width axially as shown by arrows at A than the axial width of the center channel shown at B and theaxial width of I the bottom channel shown at C. l have found that such substantial axial enlargement of the throat in the portion carrying the electrical currents which equally divide from the upper portion of the center channel is of greatest benefit in achieving maximum flow and lowest temperature differentials. In FIGS. 12 and 13 such current pattern is illustrated. It will be noted that the current path, rather than as in the prior art being in planes perpendicular to the axis, tends to diverge axially from the center plane X-X as the current emerges from the center channeLThis substantial axial enlargement A 'in the current carrying portion of the throat achieves greater velocities and a lowering of temperature patterns. Certain tests have indicated that preferably the axial widening of thethroat of that portion adjacent the upper end of the center channel should be held approximately to twice the width of the center and'bottom outwardly and upwardly gradient surfaces 50 and 5d. In the 'forms illustrated, the surfaces 5a and 5b are preferably tapered whereas the outwardly and upwardly gradient surfaces Sc and 5d are preferably curved. It will be understood that any of said gradient surfaces shown in FIGS. 4 to 6 inclusive, may ifdesired be either tapered or curved.

FIG. 7 is a perspective view disclosing in solid lines that form of the invention shown in FIGS-1,2 and 3 and in broken lines that form of the invention shown in FIGS. 4 to 6, inclusive.

In FIG. 8, a modification of the throat and channels is shown, the widened throat and channels being of circular form and the form of the throat may be varied as in other forms shown.

The FIG. 5 showing of US. Pat. No. 3,092,682 is shown as FIG. 10 herein and shows the improved temperature distribution pattern thereon. As stated in column 4, lines 45 to 56 of the patent, input averaged 14 kw., the flow was 64,200 pounds per hour or 32.l tons per hour and the maximum temperature rise was 23 F. The molten metal used in the example of the prior patent was lead. Using substantially the same prior art form and molten brass rather than lead as the metal and a power input of 800 kw. rather than 14 kw., it is to be noted that the temperature rise within the channels would in such I prior art structure be approximately 150 F. above the tem perature of the melt in the hearth'indicating minimal flow.

' pinching or kicking" which would be deleterious to the life of the equipment and would limit the maximum power input.

It has been found by tests that, in-the forms of my invention illustrated in FIGS. 4, 5 and 6, as shown in FIG. 9, the axial widening of the throat 11 adjacent the upper end of the center channel 5 effects for molten brass at an 800 kw. power level, a reduction of the maximum temperature differential from F. in FIG. ll showing to 40 F. and a greatly increased flow of 292 tons per hour. The form of FIGS. 1 to 3 leads to the same effect. Where higher power inputs are used, the advantages of the invention are obvious.

It has also been found that an inductor in accordance with the present invention will maintain a very high rate of unidirectional flow when the cross-sectional and longitudinal dimensions of the channels are increased when increasing the size of the inductor to enable a higher power input.

It will be obvious that a plurality of inductor units may be employed in a furnace and that the same may be positioned laterally of the hearth, etc. When the term bottom channel" is used herein, what is referred to is that channel which connects the lateral and center channel and is positioned farthest away from the hearth than the other channels.

What I claim is:

1. In an induction furnace of the submerged resistor type for melting metals, a hearth, a secondary loop adjacent said hearth, a throat interposed between said hearth and said secondary loop, two primary coils threading the secondary loop, said secondary loop consisting of two substantially rectangular branches formed by a central melting channel, a pair of lateral melting channels and a bottom channel; the said central and lateral channels connecting the said throat and the said bottom channel, each of the said channels having a major portion of its length of substantially uniform cross section, said throat having a portion at its intersection with the said central channel of an axial dimension substantially greater than the axial dimension of said central channel and substantially greater than the axial dimension of said bottom channel, said axial dimensions being those parallel to the axis of said primar y coils,.the molten metal flow from said central channel into said bottom channel being evenly divided flowing through each said lateral channel back into said throat and hearth.

2. The induction furnace of claim 1 wherein the temperature of the molten metal within said central channel is maintained below the temperatures of the molten metal in said bottom and lateral channels.

3. The induction furnace of claim 1 wherein said throat at its intersection with thecentral channel has a width dimension substantially greater than the width dimension of said central channel, said width dimensions being laterally normal to said axial dimension. I

4. The induction furnace of claim 1 wherein said intersection of the throat with the central channel has a gradient surface providing a gradient transition from the throat portion to the major portion of the central channel.

5. The induction furnace of claim I wherein said intersection of the throat with the central channel has a plurality of gradient surfaces providing a gradient transition from the throat portion to the major portion of the central channel.

6. The induction furnace of claim 1 wherein the axial dimension of said intersecting portion of the throat is about twice the axial dimension of said bottom channel.

7. The induction furnace of claim 3 wherein the axial dimension of said intersecting portion of the throat is about twice the axial dimension of said central channel and about twice 'the axial dimension of said bottom channel, and said width dimension of said intersecting portion of the throat is about twice the width dimension of said central channel.

8. The induction furnace of claim 1 wherein said central channel hasa substantially minor portion of its length provided with outwardly curved bottom edges, the radius of said curved bottom edges being substantially less than one-half the diameter of each said primary coil.

9. The induction furnace of claim 8 wherein each of said lateral channels has a substantially minor portion of its length provided with inwardly curved bottom edges, the radius of said curved bottom edges being substantially less than one half the diameter of each said primary coil.

10. in an induction furnace of the submerged resistor type for melting metals, a hearth; a secondary loop adjacent said hearth; a throat interposed between said hearth and said secondary loop, two primary coils threading the secondary loop; said secondary loop consisting of two substantially rectangular branches formed by a central melting channel; a pair of lateral malting channels and a bottom channel; said central and lateral channels connecting said throat and said bottom channel, each of said channels having a major portion of its length of substantially uniform cross section; a current carrying portion of saidthroat adjacent to the intersection of the throat with the central channel having an axial dimension greater than the axial dimension of said central channel and substantially greater than the axial dimension of said bottom channel, said axial dimensions being parallel to the axis of said primary coils, the molten metal flow from said central channel into said bottom channel being evenly divided flowing through each said lateral channel back into said throat and hearth.

11. The induction furnace of claim wherein said central channel has a gradient surface intersecting the current carrying portion of the throat providing a gradient transition from the current carrying throat portion to the major portion of the central channel.

12. The induction furnace of claim 10 wherein said central channel has a plurality of gradient surfaces intersecting the current carrying portion of the throat providing a gradient transition from the current carrying throat portion to the major portion of the central channel.

13. In an induction furnace of the submerged resistor type for melting metals, a hearth; a secondary loop adjacent to said hearth; a throat interposed between said hearth and said secondary loop; said secondary loop consisting of two substantially rectangular branches formed by a central melting channel, two lateral melting channels and a bottom channel; two primary coils threading the secondary loop providing a concentric electrical field within said central channel; said central and lateral channels connecting said throat and said bottom channel, each of said channels having a major portion of its length of substantially uniform cross section; a current carrying portion of said throat proximate to the intersection with said central channel of an axial dimension being substantially greater than the axial dimension of said central channel and substantially greater than the axial dimension of said bottom channel, said axial dimensions being parallel to the axis of said primary coils, the molten metal flow from said central channel into said bottom channel being evenly divided flowing through each said lateral channel back into said throat and hearth. 

1. In an induction furnace of the submerged resistor type for melting metals, a hearth, a secondary loop adjacent said hearth, a throat interposed between said hearth and said secondary loop, two primary coils threading the secondary loop, said secondary loop consisting of two substantially rectangular branches formed by a central melting channel, a pair of lateral melting channels and a bottom channel; the said central and lateral channels connecting the said throat and the said bottom channel, each of the said channels having a major portion of its length of substantially uniform cross section, said throat having a portion at its intersection with the said central channel of an axial dimension substantially greater than the axial dimension of said central channel and substantially greater than the axial dimension of said bottom channel, said axial dimensions being those parallel to the axis of said primary coils, the molten metal flow from said central channel into said bottom channel being evenly divided flowing through each said lateral channel back into said throat and hearth.
 2. The induction furnace of claim 1 wherein the temperature of the molten metal wiThin said central channel is maintained below the temperatures of the molten metal in said bottom and lateral channels.
 3. The induction furnace of claim 1 wherein said throat at its intersection with the central channel has a width dimension substantially greater than the width dimension of said central channel, said width dimensions being laterally normal to said axial dimension.
 4. The induction furnace of claim 1 wherein said intersection of the throat with the central channel has a gradient surface providing a gradient transition from the throat portion to the major portion of the central channel.
 5. The induction furnace of claim 1 wherein said intersection of the throat with the central channel has a plurality of gradient surfaces providing a gradient transition from the throat portion to the major portion of the central channel.
 6. The induction furnace of claim 1 wherein the axial dimension of said intersecting portion of the throat is about twice the axial dimension of said bottom channel.
 7. The induction furnace of claim 3 wherein the axial dimension of said intersecting portion of the throat is about twice the axial dimension of said central channel and about twice the axial dimension of said bottom channel, and said width dimension of said intersecting portion of the throat is about twice the width dimension of said central channel.
 8. The induction furnace of claim 1 wherein said central channel has a substantially minor portion of its length provided with outwardly curved bottom edges, the radius of said curved bottom edges being substantially less than one-half the diameter of each said primary coil.
 9. The induction furnace of claim 8 wherein each of said lateral channels has a substantially minor portion of its length provided with inwardly curved bottom edges, the radius of said curved bottom edges being substantially less than one-half the diameter of each said primary coil.
 10. In an induction furnace of the submerged resistor type for melting metals, a hearth; a secondary loop adjacent said hearth; a throat interposed between said hearth and said secondary loop, two primary coils threading the secondary loop; said secondary loop consisting of two substantially rectangular branches formed by a central melting channel; a pair of lateral malting channels and a bottom channel; said central and lateral channels connecting said throat and said bottom channel, each of said channels having a major portion of its length of substantially uniform cross section; a current carrying portion of said throat adjacent to the intersection of the throat with the central channel having an axial dimension greater than the axial dimension of said central channel and substantially greater than the axial dimension of said bottom channel, said axial dimensions being parallel to the axis of said primary coils, the molten metal flow from said central channel into said bottom channel being evenly divided flowing through each said lateral channel back into said throat and hearth.
 11. The induction furnace of claim 10 wherein said central channel has a gradient surface intersecting the current carrying portion of the throat providing a gradient transition from the current carrying throat portion to the major portion of the central channel.
 12. The induction furnace of claim 10 wherein said central channel has a plurality of gradient surfaces intersecting the current carrying portion of the throat providing a gradient transition from the current carrying throat portion to the major portion of the central channel.
 13. In an induction furnace of the submerged resistor type for melting metals, a hearth; a secondary loop adjacent to said hearth; a throat interposed between said hearth and said secondary loop; said secondary loop consisting of two substantially rectangular branches formed by a central melting channel, two lateral melting channels and a bottom channel; two primary coils threading the secondary loop providing a concentric electrical field wiThin said central channel; said central and lateral channels connecting said throat and said bottom channel, each of said channels having a major portion of its length of substantially uniform cross section; a current carrying portion of said throat proximate to the intersection with said central channel of an axial dimension being substantially greater than the axial dimension of said central channel and substantially greater than the axial dimension of said bottom channel, said axial dimensions being parallel to the axis of said primary coils, the molten metal flow from said central channel into said bottom channel being evenly divided flowing through each said lateral channel back into said throat and hearth. 